Bearing steel excellent in corrosion resistance

Abstract

Bearing steel containing 0.10 wt % to 0.35 wt % of C, less than 0.5 wt % of Si, 0.3 wt % to 1.5 wt % of Mn, 0.03 wt % or less of P, 0.03 wt % or less of S, 1.0 wt % to 3.5 wt % of Ni, 1.0 wt % to 5.0 wt % of Cr, 0.03 wt % to 2.5 wt % of Mo, 0.005 wt % to 0.050 wt % of Al, 0.003 wt % or less of Ti, 0.0015 wt % or less of O, 0.025 wt % or less of N, and a substantially residual part of Fe, wherein the bearing steel after carburizing or carbonitriding treatment exhibits a surface C concentration of not lower than 0.9%, contains 15% by area or less of carbide and contains 0.1% by area or less of rod-like carbide 10 having an aspect ratio of not lower than 3 in terms of the ratio of major diameter to minor diameter and having a minor diameter of not smaller than 2 μm.

What is claimed is:  
     
         1 . Bearing steel excellent in corrosion resistance comprising: 
 0.10 wt % to 0.35 wt % of C;    less than 0.5 wt % of Si;    0.2 wt % to 1.5 wt % of Mn;    0.03 wt % or less of P;    0.03 wt % or less of S;    1.0 wt % to 3.5 wt % of Ni;    1.0 wt % to 5.0 wt % of Cr;    0.03 wt % to 2.5 wt % of Mo;    0.005 wt % to 0.050 wt % of Al;    0.003 wt % or less of Ti;    0.0015 wt % or less of O;    0.025 wt % or less of N; and    a substantially residual part of Fe,    wherein the bearing steel after carburizing or carbonitriding treatment exhibits a surface C concentration of not lower than 0.7%, contains 15% or less by area of carbide and contains 0.1% or less by area of carbide having an aspect ratio of not lower than 3 in terms of the ratio of major diameter to minor diameter and having a minor diameter of not smaller than 2 μm.    
     
     
         2 . The bearing steel according to  claim 1  further comprising at least one of 0.05 wt % to 1.0 wt % of V, and 0.1 wt % or less of Nb as an alloy component.  
     
     
         3 . The bearing steel according to  claim 1 , wherein Ni is set from 2.0 wt % to 3.0 wt %.  
     
     
         4 . The bearing steel according to  claim 1 , wherein Cr is set from 1.0 wt % to 2.0 wt %.  
     
     
         5 . The bearing steel according to  claim 1 , wherein Mo is set from 0.3 wt % to 1.0 wt %.  
     
     
         6 . The bearing steel according to  claim 1 , wherein Ni is set from 2.0 wt % to 3.0 wt %, Cr is set from 1.0 wt % to 2.0 wt % and Mo is set from 0.3 wt % to 1.0 wt %.  
     
     
         7 . The bearing steel according to  claim 1 , wherein the bearing steel after carbonitriding treatment exhibits the surface C concentration of lower than 0.9%.  
     
     
         8 . The bearing steel according to  claim 2 , wherein the bearing steel after carbonitriding treatment exhibits the surface C concentration of lower than 0.9%.  
     
     
         9 . The bearing steel according to  claim 6 , wherein the bearing steel after carburizing treatment exhibits the surface C concentration of lower than 0.9%.  
     
     
         10 . The bearing steel according to  claim 1 , wherein the bearing steel after carbonitriding treatment exhibits the surface C concentration of from 0.79 to 0.82%.  
     
     
         11 . The bearing steel according to  claim 6 , wherein the bearing steel after carbonitriding treatment exhibits the surface C concentration of from 0.79 to 0.82%.  
     
     
         12 . The bearing steel according to  claim 1 , wherein the bearing steel after carburizing exhibits the surface C concentration of not lower than 0.9%.  
     
     
         13 . The bearing steel according to  claim 2 , wherein the bearing steel after carburizing exhibits the surface C concentration of not lower than 0.9%.